Ecteinascidins are a group of marine alkaloid having antineoplasticity which is isolated from the extracted products from the marine tunicate habitat of the Caribbean sea by a very small amount. Among the ecteinascidins, Et 743 has a very strong antineoplastic activity, studies to put it into practical use as a carcinostatic agent are limited, and the phase II clinical tests are now being carried out in ten countries in Europe and America. It is known that Et 743 has an effect of depressing the proliferation of cancer cells by 10 to 100 times more potent than (IC50=0.1-1 nM) Toxol, Camptotesin, Adriamycin or Mitomycin which are currently used carcinostatic agents.
From the background mentioned above, various studies for synthesis were carried out; however, the complete synthesis was only reported by Prof. E. J. Corey of Harvard University in the U.S.A. (J. Am. Chem. Soc. 1996, 118, 9202-9203, reference document A).
In the process of the total synthesis disclosed in Document A (refer to page 9202), the main feature of the process is that Et 743 is synthesized from the analogous compound to the compound represented by general formula 1 of the present invention via intermediates 4 and 8. That is, according to said process, the C4 site of ring B (regarding the location of rings, and the sites of atoms comprising the 6 membered ring, refer to general formula 1), which composes a 6 membered ring, is formed from the intermediate 4 at the first step. Since the atom C4 composing the ring B of the 6-membered ring H, which lacks reactivity, is bonded, it becomes necessary to perform an oxidation reaction at the C4 site on the B ring. This oxidation reaction is not effective and is carried out under harsh conditions; therefore production on an industrial scale is difficult, and also the yield is not good. Further, since the atom N12 site of the synthesized intermediate is substituted by an alkyl group which lacks reactivity, in this case substituted by a methyl group, it is not suited to the synthesis of various compounds. Although total synthesis was reported, the supplying source of Et 743 still depends on the natural sample whose supply is very scarce. Therefore, the establishment of the method for a large scale production of Et 743 is desired and requires accomplishing an effective synthesizing process.
Since ET 743 is known as a medicine having high antineoplasticity, and phthalascidin induced from the intermediate product at the synthesis of Et 743 displays the same activity to ET 743, the establishment of an effective and mild method for synthesis of ET 743 and analogous compounds thereof is strongly desired.
Therefore, the subject of the present invention is to accomplish the effective method for total synthesis of Et 743, and further, to provide not only Et 743 but also analogous compounds.
To dissolve the subject, the present invention uses retrosynthetic analysis for easy synthesis. It will be possible to form a B ring by a ring forming reaction at the ortho position of phenol, which binds an A ring to inner molecular aldehyde in a compound generated by the 4-8 reaction. Further, the present invention contemplates that the generated compound by the 4-8 reaction can be synthesized based on the polycondensation reaction of general formula 4, and general formula 5 via a compound of general formula 3. Then the total synthesis of Et 743, which is the aimed compound, can be accomplished by way of the compounds represented by general formulae 5, 4, 3, 2 and 1 and the specific structure of general formulae 1 and 2. This synthetic route provides for the analogous compounds of Et 743.